Metal cleaning composition and process



Patented Sept. 11, 1951 UNITED- STATES PATENT OFFICE METAL CLEANING COMPOSITION PROCESS AND Hugh Graham Webster, Detroit, Mich., assignm to J. H. Shoemaker, Detroit, Mich.

No Drawing. Application April 7, It), sel'lll N0. 739,961

4Claims. 1

This application relates to metal cleaning and is so ordinary and well known here considered as a step in the process.

"It'may be mentioned that an important dilference between the bath hereof and the bath of a prior application, Serial No. 520,332, now Patent 2,458,661, patented January 11, 1949, is that the bath hereof contains a considerably larger proportion of sodium nitrate. excess of sodium nitrate is used up in converting I believe that such the organic material, above described, to carbon dioxide, which enters the bath as a carbonate and may thus be removed. It has been found mately parts by weight of an alkali metal nitrate, such as sodium nitrate, nineteen parts by weight of an alkali metal hydroxide, such as sodium hydroxide, and one part by weight of an alkali metal chloride, 'suchas sodium the "latter being preferab in -flakeform. Theimmersionmaybeofanydesiredlength,justsolongasitissuflicienttoremove the organic surface impurities, such as that when using a bath of the prior application,

Serial No. 520,332, on automobile engine blocks which have been in use a long time, and are coated with dirt, grease, oil, etc., that after several weeks of use of such bath with such objects,

' the composition of the bath had deteriorated to those above described and to convert inorganic surface impurities, such as sulphuncarbon, etc.

to oxide form. Theoperating temperature of the bath may be any desired temperature, just 1 so long as it is above the melting point of themolten mixture. In the proportions specified above, the melting point is approximately 550 F.

The second'step of the process comprises immersing the metal removed from the first bath in a second non-electrolytic bath which is of such a nature that when the metal article is immersedinthesecondbathforanydesired and propertimeachemiealreactionwilltakeplace between the composition of the bath and the oxidized coating which willremove such oxidized coating from the metal object and thus leave the surface tree of the original impurities, the organic impurities of which had been removed, and the inorganic impm'ities of which had been transformed into oxides now being removed by the second bath.

The immersion in the second bath, however, is of such short duration as not to etch the surface and thus to expose at the surface other impurities, not previously existent, or not previously exposed. The second bath leaves the surface free of all impurities and consisting solely of the metal. The second bath is preferably a. dilute acid selected from the class of hydrochloric and sulphuric acids and the immersion in such sec- Itmaybementioned thateachstep hereof is followed by'a water rinse, but since water rinsing the point where it was no longer effective. The excess of nitrate represented by the formula herein disclosed, overcomes the weakening of the bath of the prior'application when used for the special type o'f-objects being cleaned as here described namely, objects coated with large amounts of organic materials, such as oil, grease,

road dirt,v etc. 1

Now having described the process herein disclosedfreference should be had :to the claims which follow; 1

I claim:

'1. Descaling and degreasing composition for grease and scale coated alkali resistant metals for use in moltenv bath form comprising a mixture of aboutnineteen parts by weight of alkali metal hydroxide, about nineteen parts by weight part by of alkali metal nitrate and about one weight of alkali metal chloride. 7

2. Descaling and degreasing composition for grease and scale coated alkali resistant metals for use in molten bath form comprising a mixture of about nineteen parts by weight of sodium hydroxide, about nineteen parts by weight of sodium nitrate and about one part by weight of sodium chloride.

3. A two step non-electrolytic process for cleaning the surfaces of alkali resistant metals,

having substantial amounts of oxidizable organic materials thereon, such, as oils, greases etc., as well as oxidized portions of the metal, such as scale etc., to be removed, wherein each step is in the nature of a chemical reaction, and wherein the second step leavesno added finish to the surface, and wherein the first step comprises immersing the metal in a bath comprising a molten 1 mixture of approximately l9 parts by weight of a'practice it is not alkali metal nitrate, approximately 19 parts by weight of alkali metal hydroxide and approximately 1 part by weight of alkali metal chloride, for a period of time sufficient to remove any organic surface impurities and convert inorganic surface impurities to an oxidized coating, more readily soluble than were the original inorganic impurities, the operating temperature of the first bath being above the melting point of the molten mixture, and wherein the second step comprises immersing the metal in a bath of a dilute acid selected from the class consisting of hydrochloric and sulphuric acids, whereby when the metal is immersed therein for a proper period of time, the bath will react chemically with the oxidized coating to remove it, so as to leave the surface free of the original impurities and of the oxidized coat-- ing as well, the second step, however, being such as not to expose at the surface other impurities, not previously existent, or not previously exposed, thus leaving the surface free of all impurities and consisting solely of the metal, the immersion in the second bath being sufficiently brief so as not to permit the acid to attack the metal, but merely to remove the oxidized coating formed by the first step.

4. A two step non-electrolytic process for cleaning the surfaces of alkali resistant metals, having substantial'amounts of oxidizable organic materials thereon, such as oils, greases, etc., as well as oxidized portions of the metal, such as scale, etc., to be removed, wherein each step is in the nature of a chemical reaction. and wherein the second step leaves no added finish to the surface, and wherein the first step comprises immersing the metal in a bath comprising a molten mixture of approximately 19 parts by weight of sodium nitrate, approximately 19 parts by weight of sodium hydroxide and approximately 1 part by weight of sodium chloride, for a period of time sufficient to remove any organic surface impurities and convert inorganic surface impurities to an oxidized coating, more readily soluble than were the original inorganic impurities, the operating temperature of the first bath being above the melting point of the molten mixture, and wherein the second step comprises immersing the metal in a bath of a dilute acid selected from the class consisting of hydrochloric and sulfuric acids, whereby when the metal is immersed therein for a proper period of time, the bath will react chemically with the oxidized coating to remove it, so as to leave the surface free of the original impurities and of the oxidized coating as well, the second step, however, being such as not to expose at the surface other impurities, not previously existent, or not previously expoud. thus leaving the surface free of all impurities and consisting solely of the metal, the immersion in the second bath being sufficiently brief so as not to permit the acid to attack the metal, but merely to remove the oxidized coating formed by the first step.

HUGH GRAHAM WEBSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. DESCALING AND DEGREASING COMPOSITION FOR GREASE AND SCALE COATED ALKALI RESISTANT METALS FOR USE IN MOLTEN BATH FORM COMPRISING A MIXTURE OF ABOUT NINETEEN PARTS BY WEIGHT OF ALKALI METAL HYDROXIDE, ABOUT NINETEEN PARTS BY WEIGHT OF ALKALI METAL NITRATE AND ABOUT ONE PART BY WEIGHT OF ALKALI METAL CHLORIDE.
 3. A TWO STEP NON-ELECTROLYTIC PROCESS FOR CLEANING THE SURFACES OF ALKALI RESISTANT METALS, HAVING SUBSTATIAL AMOUNTS OF OXIDIZABLE ORGANIC MATERIALS THEREON, SUCH AS OILS, GREASES ETC., AS WELL AS OXIDIZED PORTIONS OF THE METAL, SUCH AS SCALE ETC., TO BE REMOVED, WHEREIN EACH STEP IS IN THE NATURE OF A CHEMICAL REACTION, AND WHEREIN THE SECOND STEP LEAVES NO ADDED FINISH TO THE SURFACE, AND WHEREIN THE FIRST STEP COMPRISES IMMERSING THE METAL IN A BATH COMPRISING A MOLTEN MIXTURE OF APPROXIMATELY 19 PARTS BY WEIGHT OF ALKALI METAL NITRATE, APPROXIMATELY 19 PARTS BY WEIGHT OF ALKALI METAL HYDROXIDE AND APPROXIMATELY 1 PART BY WEIGHT OF ALKALI METAL CHLORIDE, FOR A PERIOD OF TIME SUFFICIENT TO REMOVE ANY ORGANIC SURFACE IMPURITIES AND CONVERT INORGANIC SURFACE IMPURITIES TO AN OXIDIZED COATING, MORE READILY SOLUBLE THAN WERE THE ORINGAL INORGANIC IMPURITIES, THE OPERATING TEMPERATURE OF THE FIRST BATH BEING ABOVE THE MELTING POINT OF THE MOLTENE MIXTURE, AND WHEREIN THE SECOND STEP COMPRISES IMMERSING THE METAL IN A BATH OF A DILUTE ACID SELECTED FROM THE CLASS CONSISTING OF HYDROCHLORIC AND SULPHURIC ACIDS, WHEREBY WHEN THE METAL IS IMMERSED THEREIN FOR A PROPER PERIOD OF TIME, THE BATH WILL REACT CHEMICALLY WITH THE OXIDIZED COATING TO REMOVE IT, SO AS TO LEAVE THE SURFACE FREE OF THE ORIGINAL IMPURITIES AND OF THE OXIDIZED COATING AS WELL, THE SECOND STEP, HOWEVER, BEING SUCH AS NOT TO EXPOSE AT THE SURFACE OTHER IMPURITIES, NOT PREVIOUSLY EXISTENT, OR NOT PREVIOUSLY EXPOSED, THUS LEAVING THE SURFACE FREE OF ALL INPURITIES AND CONSISTING OF SOLELY OF THE METAL, THE IMMERSION IN THE SECOND BATH BEING SUFFICIENTLY BRIEF SO AS NOT TO PERMIT THE ACID TO ATTACK THE METAL, BUT MERELY TO REMOVE THE OXIDIZED COATING FORMED BY THE FIRST STEP. 